Bismuth alloy impregnated grinding wheel



July 14, 1970 R. s. MEYER 3,520,666

BISMUTH ALLOY IMPREGNATED GRINDING WHEEL Filed June 14, 1967 VFYTOR F/ga/ a 5 Meyer United States Patent 3,520,666 BISMUTH ALLOY IMPREGNATEDGRINDING WHEEL Richard S. Meyer, Westfield, Mass., assignor, by mesneassignments, to American Abrasive Corporation, a corporation of DelawareFiled June 14, 1967, Ser. No. 646,068 Int. Cl. B24d 3/08 US. Cl. 51295 3Claims ABSTRACT OF THE DISCLOSURE A porous abrasive grinding wheelimpregnated with a low melting point bismuth-base alloy which acts as anelectrical conductor for use in electrolytic grinding.

In recent years, the so-called super metals, and alloys made with thesemethods, have become more and more important in space age and relatedapplications. This increased importance has given rise to many problemshowever, in that unlike standard metals and alloys, they are not readilyworkable by conventional machining techniques.

One of the problem machining areas is that of grinding parts fabricatedfrom the super metals and alloys. Particularly, it was found that theuse of the standard grinding wheels, such as aluminum oxide, siliconcarbide, and the like, was very time consuming. In attempting toovercome the time factor involved with these wheels, diamond grindingwheels were employed. While diamond grinding did reduce the time factor,cost factors and wheel reconditioning have negated its wide acceptance.

At this point, the industries involved decided that the most economicaland practical method of grinding the super metals and alloys was bymeans of electrolytic erosion or deplating.

Today, there are many electrolytic grinding wheels commerciallyavailable. A common example of these wheels may be described asvitrified aluminum oxide type which are impregnated with electricallyconductive inks. Such wheels are typified by US Pat. 3,216,854.

While most all of the electrolytic grinding wheels heretofore producedhave been sufficient to accomplish their primary purpose of grinding thesuper metals and alloys, most have given rise to problems of one kind oranother. For example, in many wheels the impregnation procedure requirescomplex high pressure equipment, or the impregnating materials areexpensive.

It is an object of the invention to provide an inexpensive yet effectiveelectrolytic grinding wheel.

It is a further object of this invention to provide an electrolyticgrinding wheel which is easily produced.

The above and other objects and advantages of the invention will becomemore clear when considered with the remaining disclosure and thedrawings, in which:

FIG. 1 is a schematic of apparatus used to produce the grinding wheelsof the present invention; and

FIG. 2 is a perspective view of a grinding wheel of the presentinvention.

Basically, this invention involves a standard grinding wheel impregnatedwith a low melting point, bismuthbase alloy that is electricallyconductive.

As is known, electrolytic grinding proceeds somewhat differently thanform grinding in the conventional manner. While an electrolytic grindingwheel is used in the conventional manner, the wheel, which has aconductive filler therein, acts as a cathode, the grinding table as ananode, and the liquid coolant as an electrolyte. Under this set-up, whencurrent is passed through the system, a deplating operation results.

3,520,666 Patented July 14, 1970 The rate of stock removed in such asystem is governed by Faradays law, rather than wheel performance, andcan be expressed as follows:

W Mlt/F j where W=weight of material removed, grams, M=atomic weight ofmaterial, grams, I=current, amperes,

t=time, second F=95,500 coulombs/gram equivalent, and j=valence ofmaterial.

From the above, it can be seen that the weight of material removed isdirectly proportional to the current supplied. Therefore, it has beenfound desirable to use a material having a low resistivity as aconductive filler in electrolytic grinding Wheels. Such materials havein the main been silver, copper and aluminum. While these materials andmixtures of same have low resistance, the cost of preparing them forimpregnation in a grinding wheel is quite expensive and calls for theuse of complex heat and pressure equipment.

In accordance with this invention, an electrolytic grinding wheel whichis produced from a standard porous abrasive wheel is impregnated with alow melting point bismuth-base alloy.

While it is realized that alloys employed in the present invention mustsacrifice some resistivity to the materials mentioned above, theadvantages gained by the use of the low melting point alloys outweighthe loss in resistivity.

In general, it has been found that bismuthbase alloys having meltingpoints of from F. to 220 F. are the most desirable from two standpoints.First, porous grinding wheels may be easily and readily impregnated withsuch alloys by the use of simple equipment; and second, the meltingpoints of such alloys permit safe handling without danger of seriousburns and/or fire in the event of accident or spillage.

As depicted in FIG. 1, the wheel 10 to be impregnated is placed betweentwo steel plates 12 and 14 having gaskets 16 and 18 thereon. The upperplate 12 has a riser pipe 20 connected thereto. Detachably mounted atthe other end of the riser pipe 20, is a pipe cap 22 and an air hose 24with a pressure regulator 26 therein.

To use the apparatus, the wheel 10 is clamped between the plates 12 and14 with its hub 13 registered with the lower end of the riser pipe 20.The complete unit is then placed in an oven at 200 F. to 210 F. to bringits temperature to a point in excess of the melting point of the alloyemployed so as to prevent solidification of the alloy duringimpregnation. After the apparatus has been uniformly heated, it isremoved from the oven and melted alloy of the type described above isadded to the riser pipe 20 and forced under pressure into the pores ofthe wheel 10, impregnating the wheel radially outwardly from the hub 13.The application of from 5 to 20 pounds of air pressure from the air hose26 has been found suitable to effect complete permeation of the wheel.When the alloy is observed to be uniformly exuding from the face of thewheel 28, the air pressure is released and the wheel is removed from theclamping apparatus and allowed to cool at room temperature. Prior tosolidification of the alloy, any excess is scraped from the sides of thewheel 10.

By the use of the above described apparatus, it was found that thepreparation of the wheels as described provides uniform distribution ofthe alloy throughout the wheel. This, of course, is highly desirable inthat the balance of the wheel is not materially affected by theimpregnation.

As mentioned above, a low melting point bismuth-base alloy is preferredin the production of the grinding wheels of this invention. Whileeutectic and non-eutectic alloys may be used, it has been found that dueto the sharp melting point characteristic of eutectic alloys, their useis preferable.

As an example of an electrolytic grinding wheel of the presentinvention, a batch of standard vitrified aluminum oxide, type 1 shapewheel, 7 inches in diameter and /2 inch thick, was impregnated with abismuth-base alloy of the following composition: 50% bismuth, 26.7%lead, 13.3% tin and 10.0 cadmium. This particular alloy is marketed bythe Cerro de Pasco Copper Corporation under the trade name Cerrobend.Being an eutectic alloy with a melting point of 158 F., it has been atraditional choice for such applications as fusible elements insprinkler heads, fire door releases, and the like.

After the above wheels had been impregnated and allowed to cool, theywere tested for rotational stress strength in accordance with therequirements of the American Standard Safety Code for the Use, Care andProtection of Abrasive Wheels. The wheels, which were designed tooperate at 7,700 s.f.p.m., were tested at 12,200 s.f.p.m. and no adverseeffect was noted. In addition, one of the wheels so produced was spintested to destruction at 20,700 s.f.p.m.

After the wheels were tested for rotational stress strength, one wasplaced on a Brown & Sharpe surface grinder adapted for electrolyticgrinding by the addition of a 150 amp Anocut Power Pack Unit. At a wheelspeed of 7,700 s.f.p.m., tool steel containing 15% tungsten was plungeground at a depth of .035 inch and 1 inch/minute traverse. During thetest, it was noted that there was no problem in drawing the fullcapacity of 150 amperes of current and that sparking was minimal.

While the above disclosure has been primarily directed to an aluminumoxide wheel impregnated with a low melting point, bismuth-base alloy, itis to be understood that other types of grinding wheels, such asvitrified silicon carbide wheels, also may be utilized.

What is claimed is:

1. In a vitrified abrasive porous grinding wheel composed of materialsselected from the group consisting of aluminum oxide and siliconcarbide, an electrically conductive impregnant, substantially fillingthe pores of said grinding wheel, comprising an alloy having a meltingpoint in the range of 130-222 F. in which the predominant material isbismuth, said alloy also containing lead, tin and cadmium.

2. In a vitrified abrasive porous grinding wheel as set forth in claim 1in which said alloy is a eutectic alloy.

3. In a vitrified abrasive porous grinding wheel as set forth in claim 1wherein the electrically conductive impregnant comprises a eutecticalloy composed of bismuth, 26.7% lead, 13.3% tin and 10.0% cadmium.

References Cited UNITED STATES PATENTS 2,340,384 2/1944 Hillix 51-3093,317,295 5/1967 Kuzmick 51309 DONALD J. ARNOLD, Primary Examiner US.Cl. X.R. 51308, 309

